The most common form of biliary tract cancer is an adenocarcinoma of the bile duct epithelium and includes cholangiocarcinoma (CCC) and gallbladder adenocarcinoma (GBC). Both diseases are characterized by an increasing incidence and poor outcome. Cholangiocarcinoma is the second most common liver cancer after hepatocellular adenocarcinoma (HCC). Cholangiocarcinoma can develop in any part of the bile duct system and is therefore classified into intrahepatic, perihilar and distal. The incidence varies extremely worldwide with the highest rates in Northeast Thailand (>80 per 100,000 population) and low rates in the Western world (0.3-3 per 100,000) (Bridgewater et al., 2014). Although it is not very common in western countries, incidence rates are increasing due to aging populations. In Germany CCC mortality more than tripled between 1998 and 2008 due to demographic changes (von Hahn et al., 2011). The average age of people diagnosed with CCC is around 70 years (American Cancer Society, 2015).
Risk factors for cholangiocarcinoma include chronic liver and bile tract diseases such as primary sclerosing cholangitis, hepatolithiasis, bile duct stones, gallbladder polyps, liver fluke infections, cirrhosis, but also infections with hepatitis B or C, inflammatory bowel diseases, older age, obesity, exposure to the radioactive substance Thorotrast, family history, diabetes and alcohol consumption (World Cancer Report, 2014).
Cholangiocarcinoma is much more common in South-East Asia where parasitic infections with Clonorchis and Opisthorchis species are endemic. Beyond these regions characterized by a high incidence of foodborne liver flukes causing chronic inflammation of the biliary tree, cholangiocarcinoma is sporadic and still rather uncommon to rare.
Cholangiocarcinoma is mostly identified in advanced stages because it is difficult to diagnose. Symptoms are unspecific and diagnosis of biliary origin remains challenging since there is no specific antigenic marker. Therefore, diagnosis of CCC requires clinical and radiological exclusion of metastasis from other sites. Rising levels of serum markers such as CA19-9 and CEA may be helpful in patients with underlying hepatic diseases (World Cancer Report, 2014).
Molecular carcinogenesis of CCC includes many known oncogenes and signaling pathways. Activating KRAS mutations, loss-of-function mutations of TP53, FGFR2 fusion genes, IDH1/2 mutations, hypermethylation of p16INK4A and SOCS3, JAK-STAT activation, over-expression of EGFR/HER2, aberrant MAPK/ERK activation and c-Met over-expression are commonly found in CCC. The link between chronic biliary infection and CCC carcinogenesis is thought to be the activation of the IL-6/STAT3 pathway. IL-6 is not only secreted by tumor cells enhancing cell growth through autocrine mechanisms but also regulates the expression of other genes, such as EGFR (World Cancer Report, 2014). However, molecular stratification based on these genetic abnormalities is not ready for clinical use (Bridgewater et al., 2014).
Cholangiocarcinoma is difficult to treat and is usually lethal. The only curative treatment option is complete resection (R0). Unfortunately, only around 30% of tumors are resectable. Most stage 0, I and II, and some stage III tumors are resectable depending on their exact location, while other stage III and most stage IV tumors are unresectable (American Cancer Society, 2015). The 5-year survival after curative resection (R0) is 40%. There is no evidence that adjuvant chemotherapy prolongs 5-year survival after tumor resection. Lymph node involvement is present in one third of patients eligible for surgical treatment and is associated with poor surgical outcome. 5-year survival after non-curative resection (R1) is 20%. Given its prognostic value, lymphadenectomy of regional lymph nodes is recommended. While N1 sometimes still is considered suitable for surgical management, for N2 and M1 disease surgery is contraindicated (Bridgewater et al., 2014).
If resection of the tumor is not feasible, treatment options are very limited. Different palliative chemotherapeutic drugs such as 5-fluorouracil, gemcitabine, cisplatin, capecitabine, oxaliplatin are in use (American Cancer Society, 2015). Standard of care for palliative chemotherapy is combination of gemcitabine and cisplatin. The median survival after chemotherapy is only 12 months.
Liver transplantation can be indicated for patients with early stage unresectable tumors but is discussed controversially.
The efficacy of biological therapies in biliary tract cancers has been mixed. Drugs targeting blood vessel growth such as Sorafenib, bevacizumab, pazopanib and regorafenib are now studied for the treatment of CCC. Additionally, drugs that target EGFR such as cetuximab and panitumumab are used in clinical studies in combination with chemotherapy (American Cancer Society, 2015). For most drugs tested so far disease control and overall survival were not improved significantly but there are further clinical trials ongoing.
Gallbladder cancer is the most common and aggressive malignancy of the biliary tract worldwide. Unspecific clinical presentation also delays diagnosis and leads to the fact that only 10% of all patients are candidates for surgery. Due to the anatomical complexity of the biliary system and the high recurrence rate surgery is only curative in the minority of cases. Risk factors are similar to CCC but GBC is three times more common in females. Additionally, to gallbladder pathologies, infections with Salmonella or Helicobacter are common risk factors. GBC is common in South Americans, Indians, Pakistani, Japanese and Koreans, while it is rare in the western world. Genetic changes in GBC are poorly understood. Molecular changes such as p53 mutation, COX2 overexpression, CDKN inactivation, KRAS mutations but also microsatellite instability are thought to be involved in GBC carcinogenesis (Kanthan et al., 2015).
As for GBC only 10% of tumors are resectable and even with surgery most progress to metastatic disease, prognosis is even worse than for CCC with a 5-year survival of less than 5%. Although most tumors are unresectable there is still no effective adjuvant therapy (Rakic et al., 2014). Some studies showed that combination of chemotherapeutic drugs or combination of targeted therapy (anti-VEGFR/EGFR) with chemotherapy led to an increased overall survival and might be promising treatment options for the future (Kanthan et al., 2015).
Due to the rarity of carcinomas of the biliary tract in general there are only a few GBC or CCC specific studies, while most of them include all biliary tract cancers. This is the reason why treatment did not improve during the last decades and R0 resection still is the only curative treatment option.
These unsatisfactory treatment options and low survival rates display the need for innovative treatment. There are some clinical studies using immunotherapy for the treatment of CCC and GBC. Success was reported when CCC with lymph node metastasis was treated by surgery and post-operative immunotherapy consisting of CD3-activated T cells and tumor lysate (Higuchi et al., 2006).
For CCC and GBC peptide-based vaccines targeting WT1, NUF2, CDH3, KIF20A, LY6K, TTK, IGF2BP3, or DEPDC1, either as triple/quadruple therapy or monotherapy combined with gemcitabine, increased overall survival about 9-12 months in phase I clinical trials. Peptide-based vaccines seem to be well tolerated, but only show a modest anti-tumor effect when administered as monotherapy. Dendritic cell-based vaccines targeting MUC1 or WT1 showed even more promising results. Therapies using cytokine induced killer cell monotherapy or tumor infiltrating lymphocytes are in phase I/II clinical trials (Marks and Yee, 2015).
Considering the severe side-effects and expense associated with treating cancer, there is a need to identify factors that can be used in the treatment of cancer in general and gallbladder cancer and cholangiocarcinoma in particular. There is also a need to identify factors representing biomarkers for cancer in general and gallbladder cancer and cholangiocarcinoma in particular, leading to better diagnosis of cancer, assessment of prognosis, and prediction of treatment success.
Immunotherapy of cancer represents an option of specific targeting of cancer cells while minimizing side effects. Cancer immunotherapy makes use of the existence of tumor associated antigens.
The current classification of tumor associated antigens (TAAs) comprises the following major groups:
a) Cancer-testis antigens: The first TAAs ever identified that can be recognized by T cells belong to this class, which was originally called cancer-testis (CT) antigens because of the expression of its members in histologically different human tumors and, among normal tissues, only in spermatocytes/spermatogonia of testis and, occasionally, in placenta. Since the cells of testis do not express class I and II HLA molecules, these antigens cannot be recognized by T cells in normal tissues and can therefore be considered as immunologically tumor-specific. Well-known examples for CT antigens are the MAGE family members and NY-ESO-1.
b) Differentiation antigens: These TAAs are shared between tumors and the normal tissue from which the tumor arose. Most of the known differentiation antigens are found in melanomas and normal melanocytes. Many of these melanocyte lineage-related proteins are involved in biosynthesis of melanin and are therefore not tumor specific but nevertheless are widely used for cancer immunotherapy. Examples include, but are not limited to, tyrosinase and Melan-A/MART-1 for melanoma or PSA for prostate cancer.
c) Over-expressed TAAs: Genes encoding widely expressed TAAs have been detected in histologically different types of tumors as well as in many normal tissues, generally with lower expression levels. It is possible that many of the epitopes processed and potentially presented by normal tissues are below the threshold level for T-cell recognition, while their over-expression in tumor cells can trigger an anticancer response by breaking previously established tolerance. Prominent examples for this class of TAAs are Her-2/neu, survivin, telomerase, or WT1.
d) Tumor-specific antigens: These unique TAAs arise from mutations of normal genes (such as β-catenin, CDK4, etc.). Some of these molecular changes are associated with neoplastic transformation and/or progression. Tumor-specific antigens are generally able to induce strong immune responses without bearing the risk for autoimmune reactions against normal tissues. On the other hand, these TAAs are in most cases only relevant to the exact tumor on which they were identified and are usually not shared between many individual tumors. Tumor-specificity (or -association) of a peptide may also arise if the peptide originates from a tumor- (-associated) exon in case of proteins with tumor-specific (-associated) isoforms.
e) TAAs arising from abnormal post-translational modifications: Such TAAs may arise from proteins which are neither specific nor overexpressed in tumors but nevertheless become tumor associated by posttranslational processes primarily active in tumors. Examples for this class arise from altered glycosylation patterns leading to novel epitopes in tumors as for MUC1 or events like protein splicing during degradation which may or may not be tumor specific.
f) Oncoviral proteins: These TAAs are viral proteins that may play a critical role in the oncogenic process and, because they are foreign (not of human origin), they can evoke a T-cell response. Examples of such proteins are the human papilloma type 16 virus proteins, E6 and E7, which are expressed in cervical carcinoma.
T-cell based immunotherapy targets peptide epitopes derived from tumor-associated or tumor-specific proteins, which are presented by molecules of the major histocompatibility complex (MHC). The antigens that are recognized by the tumor specific T lymphocytes, that is, the epitopes thereof, can be molecules derived from all protein classes, such as enzymes, receptors, transcription factors, etc. which are expressed and, as compared to unaltered cells of the same origin, usually up-regulated in cells of the respective tumor.
There are two classes of MHC-molecules, MHC class I and MHC class II. MHC class I molecules are composed of an alpha heavy chain and beta-2-microglobulin, MHC class II molecules of an alpha and a beta chain. Their three-dimensional conformation results in a binding groove, which is used for non-covalent interaction with peptides.
MHC class I molecules can be found on most nucleated cells. They present peptides that result from proteolytic cleavage of predominantly endogenous proteins, defective ribosomal products (DRIPs) and larger peptides. However, peptides derived from endosomal compartments or exogenous sources are also frequently found on MHC class I molecules. This non-classical way of class I presentation is referred to as cross-presentation in the literature (Brossart and Bevan, 1997; Rock et al., 1990). MHC class II molecules can be found predominantly on professional antigen presenting cells (APCs), and primarily present peptides of exogenous or transmembrane proteins that are taken up by APCs e.g. during endocytosis, and are subsequently processed.
Complexes of peptide and MHC class I are recognized by CD8-positive T cells bearing the appropriate T-cell receptor (TCR), whereas complexes of peptide and MHC class II molecules are recognized by CD4-positive-helper-T cells bearing the appropriate TCR. It is well known that the TCR, the peptide and the MHC are thereby present in a stoichiometric amount of 1:1:1.
CD4-positive helper T cells play an important role in inducing and sustaining effective responses by CD8-positive cytotoxic T cells. The identification of CD4-positive T-cell epitopes derived from tumor associated antigens (TAA) is of immense importance for the development of pharmaceutical products for triggering anti-tumor immune responses (Gnjatic et al., 2003). At the tumor site, T helper cells, support a cytotoxic T cell− (CTL−) friendly cytokine milieu (Mortara et al., 2006) and attract effector cells, e.g. CTLs, natural killer (NK) cells, macrophages, and granulocytes (Hwang et al., 2007).
In the absence of inflammation, expression of MHC class II molecules is mainly restricted to cells of the immune system, especially professional antigen-presenting cells (APC), e.g., monocytes, monocyte-derived cells, macrophages, dendritic cells. In cancer patients, cells of the tumor have been found to express MHC class II molecules (Dengjel et al., 2006).
Elongated (longer) peptides of the invention can act as MHC class II active epitopes.
T-helper cells, activated by MHC class II epitopes, play an important role in orchestrating the effector function of CTLs in anti-tumor immunity. T-helper cell epitopes that trigger a T-helper cell response of the TH1 type support effector functions of CD8-positive killer T cells, which include cytotoxic functions directed against tumor cells displaying tumor-associated peptide/MHC complexes on their cell surfaces. In this way tumor-associated T-helper cell peptide epitopes, alone or in combination with other tumor-associated peptides, can serve as active pharmaceutical ingredients of vaccine compositions that stimulate anti-tumor immune responses.
It was shown in mammalian animal models, e.g., mice, that even in the absence of CD8-positive T lymphocytes, CD4-positive T cells are sufficient for inhibiting manifestation of tumors via inhibition of angiogenesis by secretion of interferon-gamma (IFNγ) (Beatty and Paterson, 2001; Mumberg et al., 1999). There is evidence for CD4 T cells as direct anti-tumor effectors (Braumuller et al., 2013; Tran et al., 2014).
Since the constitutive expression of HLA class II molecules is usually limited to immune cells, the possibility of isolating class II peptides directly from primary tumors was previously not considered possible. However, Dengjel et al. were successful in identifying a number of MHC Class II epitopes directly from tumors (WO 2007/028574, EP 1 760 088 B1).
Since both types of response, CD8 and CD4 dependent, contribute jointly and synergistically to the anti-tumor effect, the identification and characterization of tumor-associated antigens recognized by either CD8+ T cells (ligand: MHC class I molecule+peptide epitope) or by CD4-positive T-helper cells (ligand: MHC class II molecule+peptide epitope) is important in the development of tumor vaccines.
For an MHC class I peptide to trigger (elicit) a cellular immune response, it also must bind to an MHC-molecule. This process is dependent on the allele of the MHC-molecule and specific polymorphisms of the amino acid sequence of the peptide. MHC-class-1-binding peptides are usually 8-14, or 8-12, or 8-11 or 8-10 amino acid residues in length and usually contain two conserved residues (“anchors”) in their sequence that interact with the corresponding binding groove of the MHC-molecule. In this way, each MHC allele has a “binding motif” determining which peptides can bind specifically to the binding groove.
In the MHC class I dependent immune reaction, peptides not only have to be able to bind to certain MHC class I molecules expressed by tumor cells, they subsequently also have to be recognized by T cells bearing specific T cell receptors (TCR).
For proteins to be recognized by T-lymphocytes as tumor-specific or -associated antigens, and to be used in a therapy, particular prerequisites must be fulfilled. The antigen should be expressed mainly by tumor cells and not, or in comparably small amounts, by normal healthy tissues. In a preferred embodiment, the peptide should be over-presented by tumor cells as compared to normal healthy tissues. It is furthermore desirable that the respective antigen is not only present in a type of tumor, but also in high concentrations (i.e. copy numbers of the respective peptide per cell). Tumor-specific and tumor-associated antigens are often derived from proteins directly involved in transformation of a normal cell to a tumor cell due to their function, e.g. in cell cycle control or suppression of apoptosis. Additionally, downstream targets of the proteins directly causative for a transformation may be up-regulated and thus may be indirectly tumor-associated. Such indirect tumor-associated antigens may also be targets of a vaccination approach (Singh-Jasuja et al., 2004). It is essential that epitopes are present in the amino acid sequence of the antigen, in order to ensure that such a peptide (“immunogenic peptide”), being derived from a tumor associated antigen, leads to an in vitro or in vivo T-cell-response.
Basically, any peptide able to bind an MHC molecule may function as a T-cell epitope. A prerequisite for the induction of an in vitro or in vivo T-cell-response is the presence of a T cell having a corresponding TCR and the absence of immunological tolerance for this particular epitope.
Therefore, TAAs are a starting point for the development of a T cell based therapy including but not limited to tumor vaccines. The methods for identifying and characterizing the TAAs are usually based on the use of T-cells that can be isolated from patients or healthy subjects, or they are based on the generation of differential transcription profiles or differential peptide expression patterns between tumors and normal tissues. However, the identification of genes over-expressed in tumor tissues or human tumor cell lines, or selectively expressed in such tissues or cell lines, does not provide precise information as to the use of the antigens being transcribed from these genes in an immune therapy. This is because only an individual subpopulation of epitopes of these antigens are suitable for such an application since a T cell with a corresponding TCR has to be present and the immunological tolerance for this particular epitope needs to be absent or minimal. In a very preferred embodiment of the invention it is therefore important to select only those over- or selectively presented peptides against which a functional and/or a proliferating T cell can be found. Such a functional T cell is defined as a T cell, which upon stimulation with a specific antigen can be clonally expanded and is able to execute effector functions (“effector T cell”).
In case of targeting peptide-MHC by specific TCRs (e.g. soluble TCRs) and antibodies or other binding molecules (scaffolds) according to the invention, the immunogenicity of the underlying peptides is secondary. In these cases, the presentation is the determining factor.